Every year, with the strangely antique but globally televised spectacle of the Oxford and Cambridge University Boat Race, cameras and crowds concentrate on the leafy curve of the Thames tideway between Putney and Chiswick. As the exhausted rowers near the end of the final stretch through Mortlake, they shoot past a gap in the river frontage commanded by one of the most uncompromising and beautiful modern houses to be built in this part of London for years. It is brand new and up for sale at around £950,000. It's called Big House.